The long-range objective of the Colorado Learning Disabilities Research Center are the identification, characterization, validation and amelioration of etiologically distinct subtypes or dimensions of learning disabilities. To accomplish these objectives, test batteries that include psychometric measures of cognitive and academic abilities (Research Project 2), reading, language and perceptual processes (Research Project 3), and ADHD and executive functions (Research Project 3 will be administered to a sample of 50 pairs of identical twins and 50 pairs of fraternal twin in which at least one member of each pair is reading disabled, to an independent sample of 50 pairs of identical twins and 50 pairs of fraternal twins in which at least one member of each pair has ADHD, and to a comparison group of 50 pairs of identical twins and 50 pairs of fraternal twins with no school history of learning disabilities or ADHD. Resulting data will be used to asses the genetic and environmental etiologies of reading deficits and ADHD, as well as their covariation with measures of mathematics performance, phonological and orthographic coding, and executive functions. In order to map major genes and/or quantitative trait loci that influence learning disabilities, blood samples will be drawn from fraternal twin pairs and subjected to genetic linkage analyses (Research Project 4). Concurrently, a longitudinal at-risk sample of 100 children will be administered differential computer-based remediation to test for possible subtype-by-treatment interactions (Research Project 5). In order to assess genetic and environmental correlates of neurobiological factors and reading deficits, MRI scans will be obtained from 100 twin pairs in which at least one member of each pair is reading disabled and from 25 pairs of control twin pairs and then subjected to state-of-the-art morphometric analyses (Research Project 6). An administrative core unit will be responsible for coordinating the activities of the six research projects; maintaining communication among the participating investigators; ascertaining and scheduling subjects; obtaining questionnaire data from families of twins; obtaining blood samples from families of fraternal twins; compiling and managing a master file of combined data sets; and administering the Center budget and other fiscal matters.